OM13008,598 NXP Semiconductors, OM13008,598 Datasheet - Page 171

• Manufacturer Part Number: OM13008,598
• Description: BOARD LPC XPRESSO LPC122X
• Manufacturer: NXP Semiconductors
• Series: LPCXpressor

Specifications of OM13008,598

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 568-6642; OM13008

NXP Semiconductors
UM10441
User manual
10.5.10.2 Auto-baud modes
Auto-baud is started by setting the ACR Start bit. Auto-baud can be stopped by clearing
the ACR Start bit. The Start bit will clear once auto-baud has finished and reading the bit
will return the status of auto-baud (pending/finished).
Two auto-baud measuring modes are available which can be selected by the ACR Mode
bit. In mode 0 the baud-rate is measured on two subsequent falling edges of the UART
RX pin (the falling edge of the start bit and the falling edge of the least significant bit). In
mode 1 the baud-rate is measured between the falling edge and the subsequent rising
edge of the UART RX pin (the length of the start bit).
The ACR AutoRestart bit can be used to automatically restart baud-rate measurement if a
time-out occurs (the rate measurement counter overflows). If this bit is set the rate
measurement will restart at the next falling edge of the UART RX pin.
The auto-baud function can generate two interrupts.
The auto-baud interrupts have to be cleared by setting the corresponding ACR
ABTOIntClr and ABEOIntEn bits.
Typically the fractional baud-rate generator is disabled (DIVADDVAL = 0) during
auto-baud. However, if the fractional baud-rate generator is enabled (DIVADDVAL > 0), it
is going to impact the measuring of UART RX pin baud-rate, but the value of the FDR
register is not going to be modified after rate measurement. Also, when auto-baud is used,
any write to DLM and DLL registers should be done before ACR register write. The
minimum and the maximum baudrates supported by UART are function of UART_PCLK,
number of data bits, stop bits and parity bits.
When the software is expecting an ”AT" command, it configures the UART with the
expected character format and sets the ACR Start bit. The initial values in the divisor
latches DLM and DLM don‘t care. Because of the ”A" or ”a" ASCII coding (”A" = 0x41,
”a" = 0x61), the UART RX pin sensed start bit and the LSB of the expected character are
delimited by two falling edges. When the ACR Start bit is set, the auto-baud protocol will
execute the following phases:
1. On ACR Start bit setting, the baud-rate measurement counter is reset and the UART
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•
ratemin
The IIR ABTOInt interrupt will get set if the interrupt is enabled (IER ABToIntEn is set
and the auto-baud rate measurement counter overflows).
The IIR ABEOInt interrupt will get set if the interrupt is enabled (IER ABEOIntEn is set
and the auto-baud has completed successfully).
RSR is reset. The RSR baud rate is switch to the highest rate.
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2 P
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16 2 15
All information provided in this document is subject to legal disclaimers.
× CLK
×
Rev. 1.1 — 10 March 2011
≤
UART baudrate
≤
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16
×
(
2
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databits
PCLK
+
paritybits
Chapter 10: LPC122x UART1
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stopbits
UM10441
© NXP B.V. 2011. All rights reserved.
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